Perhaps the most remarkable thing about Other Voices – an event that's remarkable enough in itself – is the nature of the two acts that bookend the festival, both of whom might have created uproar in the city in the not too distant past. Public Service Broadcasting, who open the first of three filmed evening showcases on the Friday night, offer music that drifts between driving and dreamy, but it's their use of 1930s and 40s public information films as both soundtrack and visual prompt that sets one thinking: how would one half of the city's population have reacted to something that could easily be taken as a nostalgic celebration of mainland Britain's former might, even if that's not their intention?

And how would the other half have reacted to the Gloaming? This transatlantic supergroup of Irish and American musicians – Iarla Ó Lionaird, Thomas Bartlett, Caoimhín Ó Raghallaigh, Martin Hayes and Dennis Cahill – whose album has been in the Irish top 10 since its release a month ago – close proceedings on Sunday with a remarkable set that sees the only standing ovation and the only encore of the weekend. Gaelic is the language and the tunes drip with the melancholy of the diaspora.

As the five musicians shift gears effortlessly through The Sailor's Bonnet, picking up the pace, feet start stamping on and off the stage, the crowd begins to whoop and one can only marvel at the intuitive understanding between the five. But it's not just jigs and reels that make them remarkable: the opening Song 44, with Bartlett holding down his piano strings to mute them, and violins scraping ominously, has more in common with post-rock than with Christy Moore. It's a staggering display of both emotion and virtuosity.

Few bands could compete with that, but on Saturday the Glaswegian trio the Amazing Snakeheads – located at a point somewhere between Alex Harvey, the Wipers and the Birthday Party – prove that it's possible to both rock and roll even in a former church, in front of an audience of ballot winners and invited dignitaries. In shiny shirts and slacks, they look like nightclub toughs from a 70s TV drama and prowl the stage like they'd be willing to offer anyone who takes a dislike to them outside. They are brutal, thrilling, transfixing and oddly uplifting: frontman Dale Barclay might portray the tough guy, but the point is that it involves the audience in the performance. Few will be neutral about this band: they'll be adored or despised.

Elsewhere, there are stirring sets from East India Youth and Colm Mac Con Iomaire, who, like the Gloaming, takes traditional music and upends it, in his case through sampling and looping his own violin and building his songs as he plays them. Bell X1 are chart-topping stars in Ireland and also-rans in the UK, and it's easy to see why in both cases. On the one hand, it's not as if there's a shortage of carefully crafted, artful and anthemic rock in the vein of Elbow or the National around in the UK; on the other, given that their set is packed with skill and melody, how come they haven't found a wide UK audience while the National have?

And, finally, a word for the band who perhaps embody the whole point of Other Voices – building connections and inspiring music. The young Dingle five-piece Walking on Cars were kids when Other Voices began in their home village, and drove them to form a band. They're clearly thrilled to be playing the Derry branch of the event, and while their drivetime pop rock may not be the height of adventure, there's a pleasing playfulness in the way it blends with R&B vocal phrasing on their opening song, See This Coming. We may yet hear more of them.